Lithium-ion secondary batteries have a higher energy density than other secondary batteries and are operable at a high voltage. Therefore, they are used for information devices such as cellular phones, as being secondary batteries that can be easily reduced in size and weight, and nowadays there is also an increasing demand for the lithium-ion secondary batteries to be used as power sources for large-scale apparatuses such as electric vehicles and hybrid vehicles.
The lithium-ion secondary batteries have a cathode layer, an anode layer, and an electrolyte layer disposed between them. An electrolyte to be employed in the electrolyte layer is, for example, a non-aqueous liquid or a solid. When the liquid is used as the electrolyte (hereinafter, the liquid being referred to as an “electrolytic solution”), it permeates into the cathode layer and the anode layer easily. Therefore, an interface can be formed easily between the electrolytic solution and active materials contained in the cathode layer and the anode layer respectively, and the battery performance can be easily improved. However, since commonly used electrolytic solutions are flammable, it is necessary to mount a system to ensure safety. On the other hand, since solid electrolytes are nonflammable, the above system can be simplified. As such, lithium-ion secondary batteries having a layer containing a nonflammable solid electrolyte have been suggested.
As a technique related to such lithium-ion secondary batteries, Patent Document 1 for example describes a bipolar secondary battery module having a bipolar secondary battery element sealed in an exterior material, the bipolar secondary battery element having a lamination, in series, of at least two or more layers of bipolar electrodes with an electrolyte layer disposed therebetween, the bipolar electrodes each having a cathode formed on one face of a current collector and an anode formed on the other face of the current collector, wherein a member having a tensile stress higher than that of the exterior material is inserted in between the bipolar secondary battery element and the exterior material.